Electric garage door openers are well known in the art. A typical electric garage door operator requires a single button for control. This single button may be either a momentary contact push-button which is hard wired to the electric garage door opener or it may be a single button on a radio frequency transmitter which transmits a signal to a radio frequency receiver in the electric garage door opener. The electric garage door operator remembers the last prior direction of operation and operates in the opposite direction upon further actuation of the single button. A typical sequence for successive actuation of the single push-button is: move in the closing direction; stop; move in the opening direction; and stop. Each actuation of the single push-button advances the operation to the next state in the sequence. This sequence repeats once it is completed. Therefore, the single button can be employed to control the opening and closing of a garage door.
The provision of electrical operators for garage doors introduces a unique safety hazard not present in manually operated doors. Electrical garage door operators do not have the discretion that a person would have to stop or alter the operation if an obstruction or hazardous condition is encountered. Instead, these electric garage door operators continue to operate unless stopped by some means built into them. One common safety hazard of electrical garage door operators is the actuation of the door for closing while inside the garage followed by an attempt to exit the garage by walking under the closing door. The person may slip and fall and be struck by the closing door. This scenario is common among small children, who may make a game of attempting to beat the door.
Typical electrical garage door operators include one or more safety systems to reduce the safety hazard. One such means is a safety strip disposed on the leading edge of the garage door. If this safety strip encounters any obstruction a switch is closed which alters the garage door opener to cause it to stop or reverse operation. Also typical of the safety features employed in such electric garage door operators are sensors that sense the mechanical tension on the drive train of the door operator. According to the prior art a cam device is connected to the drive train and pivots against a spring loaded cam follower, the cam follower mechanically coupled to a switch. If the mechanical tension on the drive train exceeds a predetermined amount then a switch is closed. The motor controller for the electric garage door operator senses the closing of the switch and initiates a safety operation. In accordance with the current state of the art, if the door were closing the motor controller would cause the garage door operator to stop, reverse direction of operation and return to the fully open position once this obstruction switch is closed. On the other hand, upon the closing of this switch when the door is opening the motor controller would merely stop the garage door. This difference in the safety operation between opening and closing of the garage door is because the opening operation of the garage door is believed safer than the closing operation. Another typical obstruction sensing device employs a light beam directed across the garage door opening. If this light beam is broken by an object the obstruction sensing device generates a signal to stop or reverse the garage door operation. Such light beam obstruction sensing devices require accurate positioning and aiming of the light source to enable proper operation and to provide the safety desired.
All of these safety features leave something to be desired as it is still possible for the operation to be hazardous even with these safety features. It would be desirable to require some attention by the operator throughout the whole action of the electric garage door operator, particularly when the door is being closed so that the operator can detect an unsafe condition.